MSc Thesis

During the period of April – August 2018, I was fortunate enough to be given the opportunity to complete my dissertation project with the GTK in Finnish Lapland. My thesis, titled “Hyperspectral characterisation of granitoid-related
Fe-Au-(Cu) mineralisation, Mäkärä,
Finnish Lapland”.

The following sections from my thesis are heavily condensed, therefore, if you would like a full copy of my report to read through, please do get in touch here.

Abstract:

Large ore deposits are becoming increasingly difficult to discover close to the surface and are commonly obscured by several hundred meters of barren, or weakly altered country rock. With drilling costs too expensive to warrant large amounts of invasive investigation, there is a call for the development of a greater understanding of hydrothermal alteration mineralogy, and in doing so, to generate new distal ore vectoring tools.

At Mäkärä, Finnish Lapland, identified as a magmatic-hydrothermal, quartz-haematite breccia-hosted gold deposit, SWIR spectroscopy is employed in order to resolve a more detailed understanding of the prospect, and generate a more robust genetic model. In doing so, this project also aims to evaluate the effectiveness of spectral indices in characterising ore mineralisation in previously under-investigated Palaeoproterozoic terranes.

Throughout the zoned hypogene geochemical dispersion halo of large magmatic-hydrothermal ore deposits, reflective alteration minerals show systematic variability in mineral chemistry. These changes manifest as subtle, but measurable variance in distinguishing SWIR absorption features. This study has effectively implemented two spectral indices, showing clear, systematic variation throughout the Mäkärä prospect – the White Mica Tschermak Substitution Index and the Kübler Illite Crystallinity Index.

Consolidation of spectral, whole rock geochemical, petrographic, EPMA chemistry, and XRD mineralogical data has alluded to the possibility of a regional magmatic hydrothermal mineralising regime, attributed to the emplacement of the post-orogenic, A-type Nattannen granitoids. The proposed genetic model involves the redistribution of elements controlled by near-neutral pH, highly oxidising, late-stage magmatic-meteoric hybrid hydrothermal fluids. A fluid mixing model is invoked as the fundamental ligand destabilisation method, pH neutralisation identified as the fundamental precipitative mechanism. Au-chloride complex destabilisation occurs at moderately neutral pH, with physical adsorption onto sulphide mineral surfaces.

Through integration with regional airborne geophysics and till geochem data, a number of new targets have been identified at Mäkärä. These are focussed along the strike of the currently delineated zone of mineralisation, and along sub-parallel structures, exhibiting similarities in key spectral features.